/*
 * Copyright (C) 2005 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define LOG_TAG "sharedbuffer"

#include "SharedBuffer.h"

#include <stdlib.h>
#include <string.h>

#include <utils/Log.h>

// ---------------------------------------------------------------------------

namespace android {

    SharedBuffer* SharedBuffer::alloc(size_t size)
    {
        // Don't overflow if the combined size of the buffer / header is larger than
        // size_max.
        LOG_ALWAYS_FATAL_IF((size >= (SIZE_MAX - sizeof(SharedBuffer))),
                            "Invalid buffer size %zu", size);

        SharedBuffer* sb = static_cast<SharedBuffer *>(malloc(sizeof(SharedBuffer) + size));
        if (sb) {
            // Should be std::atomic_init(&sb->mRefs, 1);
            // But that generates a warning with some compilers.
            // The following is OK on Android-supported platforms.
            sb->mRefs.store(1, std::memory_order_relaxed);
            sb->mSize = size;
        }
        return sb;
    }


    void SharedBuffer::dealloc(const SharedBuffer* released)
    {
        free(const_cast<SharedBuffer*>(released));
    }

    SharedBuffer* SharedBuffer::edit() const
    {
        if (onlyOwner()) {
            return const_cast<SharedBuffer*>(this);
        }
        SharedBuffer* sb = alloc(mSize);
        if (sb) {
            memcpy(sb->data(), data(), size());
            release();
        }
        return sb;
    }

    SharedBuffer* SharedBuffer::editResize(size_t newSize) const
    {
        if (onlyOwner()) {
            SharedBuffer* buf = const_cast<SharedBuffer*>(this);
            if (buf->mSize == newSize) return buf;
            // Don't overflow if the combined size of the new buffer / header is larger than
            // size_max.
            LOG_ALWAYS_FATAL_IF((newSize >= (SIZE_MAX - sizeof(SharedBuffer))),
                                "Invalid buffer size %zu", newSize);

            buf = (SharedBuffer*)realloc(buf, sizeof(SharedBuffer) + newSize);
            if (buf != NULL) {
                buf->mSize = newSize;
                return buf;
            }
        }
        SharedBuffer* sb = alloc(newSize);
        if (sb) {
            const size_t mySize = mSize;
            memcpy(sb->data(), data(), newSize < mySize ? newSize : mySize);
            release();
        }
        return sb;
    }

    SharedBuffer* SharedBuffer::attemptEdit() const
    {
        if (onlyOwner()) {
            return const_cast<SharedBuffer*>(this);
        }
        return 0;
    }

    SharedBuffer* SharedBuffer::reset(size_t new_size) const
    {
        // cheap-o-reset.
        SharedBuffer* sb = alloc(new_size);
        if (sb) {
            release();
        }
        return sb;
    }

    void SharedBuffer::acquire() const {
        mRefs.fetch_add(1, std::memory_order_relaxed);
    }

    int32_t SharedBuffer::release(uint32_t flags) const
    {
        const bool useDealloc = ((flags & eKeepStorage) == 0);
        if (onlyOwner()) {
            // Since we're the only owner, our reference count goes to zero.
            mRefs.store(0, std::memory_order_relaxed);
            if (useDealloc) {
                dealloc(this);
            }
            // As the only owner, our previous reference count was 1.
            return 1;
        }
        // There's multiple owners, we need to use an atomic decrement.
        int32_t prevRefCount = mRefs.fetch_sub(1, std::memory_order_release);
        if (prevRefCount == 1) {
            // We're the last reference, we need the acquire fence.
            atomic_thread_fence(std::memory_order_acquire);
            if (useDealloc) {
                dealloc(this);
            }
        }
        return prevRefCount;
    }


}; // namespace android